Here’s the current leaderboard of the top registrars in terms of total .com registrations as of the end of December 2017. There were approximately 135.5 million total .com domains registered as of the end of January:

Many domain companies have multiple accreditations and I’ve tried to capture the largest ones. See the notes below and let me know if I’ve missed any large registrars.

* Includes GoDaddy and Wild West Domains
** Includes Tucows and Enom
+ Includes PDR, Domain.com, FastDomain and Bigrock. There are other Endurance registrars, but these are the biggest.
++ Includes Network Solutions and Register.com